Compression self-ignition engines as represented by a diesel engine generally have higher fuel efficiency and lower CO2 emission than spark-ignition engines such as a gasoline engine. As a result, compression self-ignition engines are becoming widely prevalent as vehicular engines.
An effective way to further reduce CO2 with such a compression self-ignition engine is to adopt so-called idle stop control in which the engine is automatically stopped during an idle operation or the like and subsequently automatically restarted when a starting operation of a vehicle or the like is performed. Various studies regarding idle stop control are underway.
For example, Patent Document 1 below discloses a diesel engine controller which automatically stops the diesel engine when a given automatic stop condition is satisfied and executes fuel injection while driving a starter motor to restart the diesel engine when a given restart condition is satisfied, wherein a cylinder to which fuel is injected first is variably set based on a piston stop position of a Compression-Stop Cylinder that is a cylinder in a compression stroke during stop (upon completion of engine stop).
Specifically, in Patent Document 1, when the diesel engine is automatically stopped, a piston position of the Compression-Stop Cylinder that is in a compression stroke at that point is determined, and a judgment is made on whether or not the piston position is at an appropriate position determined in advance (for example, a range from 120 to 100 CA degrees before compression top dead center). If the piston position is at an appropriate position, initial fuel is injected into the Compression-Stop Cylinder, and if the piston position is on the top dead center-side of the appropriate position, initial fuel is injected into an Intake-Stroke Cylinder that is a cylinder in an intake stroke during stop.
With such a configuration, when the piston of the Compression-Stop Cylinder is at the appropriate position, fuel can be injected into the Compression-Stop Cylinder to reliably self-ignite the fuel and, as a result, restart the engine in a relatively short period of time. On the other hand, when the piston of the Compression-Stop Cylinder is offset from the appropriate position to the side of the top dead center, due to an insufficient compression allowance of the piston and a failure of the air inside the cylinder to reach a sufficiently high temperature, there is a risk of misfire occurring even if fuel is injected into the Compression-Stop Cylinder. Therefore, in such a case, by injecting fuel into the Intake-Stop Cylinder instead of the Compression-Stop Cylinder, air inside the cylinder can be sufficiently compressed and the fuel can be self-ignited in a reliable manner.